Anax and Cymede & Kynaios and Tiro’s last ability goes on the stack and resolves before the spell that caused it to trigger. It resolves even if that spell is countered or otherwise left the stack.

Anax and Cymede & Kynaios and Tiro’s last ability will trigger only once per spell, even if that spell targets Anax and Cymede & Kynaios and Tiro multiple times.

Anax and Cymede & Kynaios and Tiro’s last ability won’t trigger when a copy of a spell is created on the stack targeting Anax and Cymede & Kynaios and Tiro or when a spell’s targets are changed to include Anax and Cymede & Kynaios and Tiro.

Playtest cards aren’t legal for play in any tournament format other than Mystery Booster Limited formats. On the other hand, we expect they will spice up a wide variety of non-tournament games (as long as everyone’s on the same page about using them!).

Playtest cards use a modified version of game symbols, such as {T} and {W}. These modified symbols should be treated as the standard symbols during play.

For many playtest cards, you’ll need to make a generous assumption that basic game rules would be updated to allow them to work. The Mystery Booster 2 Playtest Card Notes section (reproduced here in individual Gatherer rulings) provides guidance for fitting these cards into the existing rules structure.